Nouveau - Mar 2023 - [PATCH 6.2 regression fix] drm/nouveau/kms: Fix backlight registration

The nouveau code used to call drm_fb_helper_initial_config() from
nouveau_fbcon_init() before calling drm_dev_register(). This would
probe all connectors so that drm_connector->status could be used during
backlight registration which runs from nouveau_connector_late_register().

After commit 4a16dd9d18a0 ("drm/nouveau/kms: switch to drm fbdev
helpers")
the fbdev emulation code, which now is a drm-client, can only run after
drm_dev_register(). So during backlight registration the connectors are
not probed yet and the drm_connector->status == connected check in
nv50_backlight_init() would now always fail.

Replace the drm_connector->status == connected check with
a drm_helper_probe_detect() == connected check to fix nv_backlight
no longer getting registered because of this.

Fixes: 4a16dd9d18a0 ("drm/nouveau/kms: switch to drm fbdev helpers")
Link: https://gitlab.freedesktop.org/drm/nouveau/-/issues/202
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/nouveau/nouveau_backlight.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c
b/drivers/gpu/drm/nouveau/nouveau_backlight.c
index 40409a29f5b6..91b5ecc57538 100644
--- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
+++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
@@ -33,6 +33,7 @@
 #include <linux/apple-gmux.h>
 #include <linux/backlight.h>
 #include <linux/idr.h>
+#include <drm/drm_probe_helper.h>
 
 #include "nouveau_drv.h"
 #include "nouveau_reg.h"
@@ -299,8 +300,12 @@ nv50_backlight_init(struct nouveau_backlight *bl,
 	struct nouveau_drm *drm = nouveau_drm(nv_encoder->base.base.dev);
 	struct nvif_object *device = &drm->client.device.object;
 
+	/*
+	 * Note when this runs the connectors have not been probed yet,
+	 * so nv_conn->base.status is not set yet.
+	 */
 	if (!nvif_rd32(device, NV50_PDISP_SOR_PWM_CTL(ffs(nv_encoder->dcb->or) -
1)) ||
-	    nv_conn->base.status != connector_status_connected)
+	    drm_helper_probe_detect(&nv_conn->base, NULL, false) !=
connector_status_connected)
 		return -ENODEV;
 
 	if (nv_conn->type == DCB_CONNECTOR_eDP) {
-- 
2.39.1

Reviewed-by: Lyude Paul <lyude at redhat.com>

(Also note to Mark: this is my way of letting you know someone fixed the
regression with backlight controls upstream, looking into the weird bright
screen after resume issue)

On Sun, 2023-03-26 at 22:54 +0200, Hans de Goede wrote:
> The nouveau code used to call drm_fb_helper_initial_config() from
> nouveau_fbcon_init() before calling drm_dev_register(). This would
> probe all connectors so that drm_connector->status could be used during
> backlight registration which runs from nouveau_connector_late_register().
> 
> After commit 4a16dd9d18a0 ("drm/nouveau/kms: switch to drm fbdev
helpers")
> the fbdev emulation code, which now is a drm-client, can only run after
> drm_dev_register(). So during backlight registration the connectors are
> not probed yet and the drm_connector->status == connected check in
> nv50_backlight_init() would now always fail.
> 
> Replace the drm_connector->status == connected check with
> a drm_helper_probe_detect() == connected check to fix nv_backlight
> no longer getting registered because of this.
> 
> Fixes: 4a16dd9d18a0 ("drm/nouveau/kms: switch to drm fbdev
helpers")
> Link: https://gitlab.freedesktop.org/drm/nouveau/-/issues/202
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_backlight.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c
b/drivers/gpu/drm/nouveau/nouveau_backlight.c
> index 40409a29f5b6..91b5ecc57538 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
> @@ -33,6 +33,7 @@
>  #include <linux/apple-gmux.h>
>  #include <linux/backlight.h>
>  #include <linux/idr.h>
> +#include <drm/drm_probe_helper.h>
>  
>  #include "nouveau_drv.h"
>  #include "nouveau_reg.h"
> @@ -299,8 +300,12 @@ nv50_backlight_init(struct nouveau_backlight *bl,
>  	struct nouveau_drm *drm = nouveau_drm(nv_encoder->base.base.dev);
>  	struct nvif_object *device = &drm->client.device.object;
>  
> +	/*
> +	 * Note when this runs the connectors have not been probed yet,
> +	 * so nv_conn->base.status is not set yet.
> +	 */
>  	if (!nvif_rd32(device,
NV50_PDISP_SOR_PWM_CTL(ffs(nv_encoder->dcb->or) - 1)) ||
> -	    nv_conn->base.status != connector_status_connected)
> +	    drm_helper_probe_detect(&nv_conn->base, NULL, false) !=
connector_status_connected)
>  		return -ENODEV;
>  
>  	if (nv_conn->type == DCB_CONNECTOR_eDP) {
-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat